School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ, USA.
School for Engineering of Matter, Transport, and Energy, Arizona State University, 551 E Tyler Mall, Tempe, AZ, 85287, USA.
Ann Biomed Eng. 2018 Dec;46(12):2048-2056. doi: 10.1007/s10439-018-2092-9. Epub 2018 Jul 12.
Ankle stiffness has been known as one of the most important components contributing to the maintenance of lower body stability during postural balance and locomotion. It has been repeatedly shown that women have lower stability and increased risk of injury when compared to men participating in similar sports activities, yet sex differences in neuromuscular control of the ankle, including the modulation of ankle stiffness, and their contribution to stability remain unknown. To identify sex differences in human ankle stiffness, this study quantified multi-dimensional ankle stiffness in 20 young, healthy men and 20 young, healthy women over a range of ankle muscle contractions, from relaxed to 20% of maximum voluntary co-contraction of ankle muscles. A wearable ankle robot and a system identification method were used to reliably quantify ankle stiffness in a 2-dimensional space spanning the sagittal plane and the frontal plane. In all muscle activation levels, significant sex differences in ankle stiffness were identified in both the sagittal and frontal planes. In the given experimental conditions, ankle stiffness in males was higher than females up to 15.1 and 8.3 Nm/rad in the sagittal plane and the frontal plane, respectively. In addition, sex differences in the spatial structure of ankle stiffness were investigated by quantifying three parameters defining the stiffness ellipse of the ankle: area, aspect ratio, and orientation. In all muscle activation levels, a significant sex difference was identified in the area of stiffness ellipse as expected from the sex difference in the sagittal and frontal planes. However, no statistical sex difference was observed in the aspect ratio and orientation, which would be due to little differences in major anatomical configurations of the ankle joint between sexes. This study, in combination with future studies investigating sex differences during dynamic tasks (e.g. postural balance and locomotion) would serve as a basis to develop a risk assessment tool and sex-specific training programs for efficient ankle injury prevention or rehabilitation.
踝关节僵硬已被认为是维持姿势平衡和运动时下半身稳定性的最重要组成部分之一。已经反复表明，与从事类似体育活动的男性相比，女性的稳定性较低，受伤风险更高，但踝关节神经肌肉控制的性别差异，包括踝关节刚度的调节，以及它们对稳定性的贡献仍不清楚。为了确定踝关节刚度的性别差异，本研究在 20 名年轻健康男性和 20 名年轻健康女性中量化了踝关节刚度的多维特性，这些参与者的踝关节肌肉收缩范围从放松到 20%的最大自主协同收缩。使用可穿戴式踝关节机器人和系统识别方法，在跨越矢状面和额状面的二维空间中可靠地量化踝关节刚度。在所有肌肉激活水平下，在矢状面和额状面都观察到踝关节刚度存在显著的性别差异。在给定的实验条件下，男性的踝关节刚度在矢状面和额状面分别比女性高 15.1 和 8.3 Nm/rad。此外，通过量化定义踝关节刚度椭圆的三个参数：面积、纵横比和方向，研究了踝关节刚度空间结构的性别差异。在所有肌肉激活水平下，正如预期的那样，在矢状面和额状面存在性别差异，因此刚度椭圆的面积存在显著的性别差异。然而，在纵横比和方向方面没有观察到统计学上的性别差异，这可能是由于男女踝关节的主要解剖结构差异较小。这项研究，结合未来研究动态任务（如姿势平衡和运动）中的性别差异，将为开发风险评估工具和针对特定性别的训练计划提供依据，以有效预防或康复踝关节损伤。
